Modern medicine employs many medical procedures where electrical signals or currents are received from or delivered to a patient's body. The interface between medical equipment used in these procedures and the skin of the patient usually includes a biomedical electrode. Such an electrode typically includes a conductor connected electrically to the equipment and a conductive medium adhered to or otherwise in contact with the patient's skin. Biomedical electrodes have been included as a part of therapeutic as well as diagnostic medical procedures and equipment.
Therapeutic devices and procedures using those devices make use of biomedical electrodes. For example, such electrodes are employed in transcutaneous electronic nerve stimulation (TENS) devices for pain management; neuromuscular stimulation (NMS) techniques for treating conditions such as scoliosis; defibrillation electrodes for dispensing electrical energy to a chest cavity to defibrillate the heart; and dispersive electrodes to receive electrical energy dispensed into an incision made during electrosurgery.
Diagnostic procedures that make use of biomedical electrodes include electrocardiography for monitoring heart activity and diagnosing heart abnormalities. Examples of diagnostic biomedical electrodes include those described in U.S. Pat. No. 4,352,359 to Larimore; U.S. Pat. No. 4,524,087 to Engel; U.S. Pat. No. 4,539,996 to Engel; U.S. Pat. No. 4,554,924 to Engel; U.S. Pat. No. 4,848,348 to Carim; U.S. Pat. No. 4,848,353 to Engel; U.S. Pat. No. 5,012,810 to Strand et al.; U.S. Pat. No. 5,133,356 to Bryan et al.; U.S. Pat. No. 5,215,087 to Anderson et al.; and U.S. Pat. No. 5,296,079 to Duan et al.
For diagnostic applications, non-polarizable electrodes, and in particular electrodes comprised of silver and/or silver chloride, have become the current collectors of choice because of their high electrical stability. In low-cost versions, such electrodes are often coated in thin sections onto an insulating backing from a conductive ink containing silver/silver chloride particles and a polymeric binder. While silver/silver chloride electrodes are resistant to corrosive attack and generally have a long shelf-life, under certain gel conditions (e.g., at a low pH in conjunction with a high water content and high chloride concentration), they can undergo accelerated corrosion and exhibit premature electrical failure. Attempts to address the problem of undesired corrosion and failure include the use of sacrificial anodes interwoven into an electrode assembly and electrically connected to a current collector. While functional, the use of sacrificial anodes is generally not cost-effective due to added material costs and certain design constraints. Another method for inhibiting corrosion has been the addition of organic agents as corrosion retarding agents to the silver/silver chloride matrix. The use of corrosion retarding agents is disclosed in copending and coassigned U.S. Patent Application 20030045788 by Menon et al, entitled “Corrosion Prevention In Biomedical Electrodes.”
Additionally, other materials have been proposed as alternatives for traditional silver and/or silver chloride electrode materials. Exemplary of such alternate materials include those comprised of titanium hydride and certain carbon-containing materials. However, electrodes incorporating these alternative materials are often complex, making them more expensive to manufacture.
While the art has focused on how to protect or substitute silver or silver chloride materials in biomedical electrodes, it has not provided a means to avoid corrosion altogether while continuing to use silver/silver chloride as conductive electrode materials. Some effort has been made to formulate conductive adhesives using antioxidants, for example. While such measures are intended to eliminate the corrosion problem, they have been less than effective, especially when “bicontinuous” adhesives having both hydrophilic and hydrophobic regimes are used. Therefore, a need remains for corrosion-resistant biomedical electrodes employing silver/silver chloride that are relatively easy to construct and remain relatively cost-effective.
While not intending to be bound by theory, it is known that peroxides are produced in conductive adhesives that are used to adhere biomedical electrodes to mammalian skin. The formation of peroxides is generally attributed to the process employed to “age” or condition the electrodes prior to use. It has been postulated that the formation of such peroxides is a factor in the onset of corrosion in biomedical electrodes, especially silver/silver chloride biomedical electrodes. In particular, the aging process for electrodes comprising bicontinuous conductive adhesives is believed to produce significant amounts of oxidizing peroxides because certain surfactants normally included in such adhesive formulations are abundant and of a type that can react to produce such peroxides.
It has now been unexpectedly discovered that a unique class of materials act as peroxide scavengers when used as additives in conductive adhesives, including bicontinuous adhesives, to significantly reduce the onset of corrosion in biomedical electrodes.